Color coding carbide

ABSTRACT

The present invention enables one to easily and immediately distinguish between grades, dimensions and manufacturers of cemented carbide by color coding. This invention further provides for a semi-permanent coloration of the carbide and this coloration does not interfere with the brazing process. When the process disclosed here is applied to carbide parts, the coloration can be used as a means to distinguish between grades of carbide or to classify visually indistiguishable dimensional changes. In addition, the coloration can provide a record of the manufacturing origin of each individual carbide part.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF INVENTION

[0003] Cemented carbide, or ‘carbide’, is made by combining very hard tungsten carbide (WC) in a matrix of cobalt (Co) via liquid phase sintering. At high temperatures, WC has high solubility in Co and is wet by the liquid Co binder. The resultant material combines high strength, toughness and hardness and is widely used for cutting tools and in wear resistant applications.

[0004] There are many different grades of carbide developed for various applications. Different grades are manufactured by varying the amount of Co in the binder, alloying the binder with different metals, varying the WC grain size and by depositing surface coatings. Often, the carbide part will be used as a tool bit and brazed onto a tool, such as in carbide-tipped saw blades or cutting tools.

[0005] One problem with the use of various carbide grades in practice is the potential to mix up pieces of carbides since most grades are visibly indistinguishable. The current method to identify grades is by labeling the containers holding them or by individually engraving each piece. Alternatively, metallurgical analysis can be used to determine the composition and grain size of unknown carbide, but this requires time and is costly. There is currently no reliable, quick, economical method used to distinguish among unlabelled carbide pieces, which results in scrapped material.

[0006] Another difficulty when working with carbide is the inability to quickly distinguish among various sizes of parts. Typically, carbide parts are manufactured to exact dimensional sizes. Users will utilize multiple sized carbide parts, each for a different, specific application. Since these carbide parts will only vary very slightly dimensionally, they are very easy to mix up. For example, a manufacturer may be using carbide to tip various specific cutting tools, where each tip only varies by a few thousandths of an inch in thickness. While it is possible to individually measure each carbide tip, it is unreliable to classify the tips by thickness visually.

[0007] Another problem encountered by manufacturers and users of carbide parts is the inability to distinguish between the origin of the parts. That is, it is desirable for manufacturers to be able to imbue a marking to distinguish its parts from those of other manufacturers.

[0008] There is clearly a need, therefore, to quickly and easily distinguish amongst various carbide grades, dimensions and manufacturers. Often, carbide parts are used as tips on larger tools, and are attached via brazing. It is also important, therefore, that the method used to fufill this need does not diminish the brazeability or strength of the brazed joint.

[0009] The present invention enables one to easily and immediately distinguish between grades, dimensions and manufacturers of carbide. This invention further provides for a semi-permanent coloration of the carbide, thus preventing the scrapping of unknown material. Importantly, the coloration does not interfere with the brazing process. When the process disclosed here is applied to carbide parts, the coloration can be used as a means to distinguish between grades of carbide. Alternatively, different colors can be used to classify between dimensional changes. This is particularly useful in a manufacturing operation where multiple, very close and visually indistinguishable sized carbide parts are used. Finally, the coloration can provide a record of the manufacturing origin of each individual carbide part.

[0010] The carbide coloration of the present invention is obtained via a two-step process. First, the surface of the carbide is enriched with metal and second; the metal-enriched surface is chemically treated.

[0011] Although there appears to be no directly related prior art, one of the embodiments uses a process described by U.S. Pat. No. 2,979,811. In this process, carbide is processed through a number of steps involving molten salt bath heat treatment and chemical exposure. The process is used to wick a thin (4-6 micron) layer of pure Co from the bulk carbide binder phase to the surface of the carbide. This surface layer improves capillary action between the braze metal and the carbide improving brazeability. In addition, some Co diffuses into the braze, improving the strength of the bond. As related to this invention, the surface enrichment with Co as applied by U.S. Pat. No. 2,979,811 can be used to prepare the surface of the carbide for the coloring procedure.

[0012] Although various methods can be used to enrich the surface layer of the carbide with metal, one of these methods involves the plating of metal. While plating of metal may have first been applied in antiquity, there are many more recent examples of prior art. Often cited in the literature is the discussion by Schock, et. al, (Trans. Electrochemical Society, vol. XI, 1907, pp. 136-139). This was followed by a number of patents including U.S. Pat. Nos. 1,564,581, 2,419,231, and 2,497,905 that teach the electroplating of zinc. In addition, U.S. Pat. No. 2,327,002 teaches the use of oxide coatings. These early examples of prior art each teach the advantages of corrosion resistance and/or abrasion resistance with the additions of coatings. However, none of them are applicable to coatings on carbide and none of them teach to utilize the coating as an intermediate step for colorization. Many more recent patents, and commercial processes, teach specific formulations or coating processes, but none teach the use of a coating on a carbide to be used as an identifier.

[0013] While a number of chemical processes can be used to add coloration to the carbide that has been enriched at the surface with metal, one method is the use of chemical conversion coatings. Perhaps first described in German patent 423758, a chromate conversion coating was described for coating aluminum alloys. This coating was used primarily to enhance the corrosion resistance of the substrate. Many different formulations and processes to apply the coatings were also developed, including those taught by U.S. Pat. No. 2,438,887 and numerous commercial applications. In none of the literature, however, is the use of a conversion coating described as a means of color coding a metal layer on a carbide substrate.

[0014] It appears therefore that while each of the two steps described as part of the present invention have been separately described previously, they have not been used on carbides, nor have they been used together, nor have they been used to provide a means to quickly and easily distinguish amongst various carbide forms.

[0015] While carbide parts can be colored by painting, this method has a number of drawbacks, which is why it has not experienced widespread use. It is difficult to obtain a visually pleasing appearance on a painted carbide and surfaces with widely varying paint thicknesses often result. In addition, most paints will volatilize when exposed to temperatures experienced during brazing, which results in a poor integrity braze joint. Finally, painted surfaces can be easily chipped during handling or removed upon contact with many chemicals or solvents, thus reducing or eliminating their effectiveness as an identifier.

BRIEF SUMMARY OF THE INVENTION

[0016] The present invention provides for a process in which carbide grades can easily be identified, regardless of grade, geometry or source of manufacture. In one embodiment, the surface layer of the carbide is enriched with metal, which is in turn chemically treated to provide coloration. The metal-enrichment process can be obtained via several methods. These include heat-treatments to diffuse metal from the carbide's binder phase to the surface, electrolytic or electroless plating, and vapor deposition. The coloration process can also occur via several methods, including chromate conversion coating, and oxide or phosphate conversion coating.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0017] Not Applicable

DETAILED DESCRIPTION OF THE INVENTION

[0018] According to the present invention, carbide parts can be color coded to provide a method to easily visually distinguish among grades, sizes or forms of carbide. The coloration of the surface occurs as the result of an interaction between a chemical solution and the surface of the carbide that has been enriched with metal. Various chemical solutions can be used such as those comprised of chromate, phosphate, oxide, as well as others. Typically, this type of chemical interaction is referred to as conversion coating, although other methods may be employed. The enrichment of the surface with metal, or metals, can be accomplished by various methods, including diffusion and/or plating procedures.

[0019] In one embodiment of this invention, the surface of the carbide is enriched with metal via an electrolytic plating process. In another embodiment, the surface is enriched via heat treatment. Heat treatment can enrich the surface by effectively diffusing metal(s) in the binder phase of the cemented carbide to the surface. In yet another embodiment, the surface is enriched via an electroless plating process. In yet another embodiment, the surface is enriched via plasma or chemical vapor deposition.

EXAMPLE 1

[0020] Carbide pieces were yellow color coded after electrolytically plating zinc onto the surface via the following procedure:

[0021] a) Soak for two minutes in 25% HCl aqueous solution,

[0022] b) Water rinse,

[0023] c) Plate in acid zinc bath (containing KCl, boric acid, Zn, and wetting agent) at 7 volts for 15 minutes,

[0024] d) Water rinse,

[0025] e) Dip for ten seconds in 2% HNO₃,

[0026] f) Water rinse,

[0027] g) Soak in a 1% aqueou Iridite™ 80 solution for 15-20 seconds,

[0028] h) Water rinse,

[0029] i) Dry.

[0030] As demonstrated by example 1, the surface of the carbide was enriched with metal (zinc) via a plating reaction, and this surface was then successfully colored via a conversion coating process. In this example, steps a) through d) detail the plating process, and steps e) through i) detail the coloring process. The key to the coloration process is in step g) in which the example utilizes a commercial chromate conversion coating. The color of the carbides can be altered by the use of various chromate solutions. For example, a solution containing the commercial product Iridite™ 80 will result in a yellow color, while a solution containing Macrobrite™ 16 results in a clear color. There are a number of other commercially available chromate conversion coating solutions which will result in other colors. In addition, a multitude of colors are available via the use of several commercially available chromate dyes. These dyes would be applied immediately following the conversion coating process, and before the carbide parts are dried.

[0031] Although the example disclosed here utilizes an electrolytic plating process to apply zinc metal to the surface of the carbide part, it is acknowledged that several alternate methods of plating or otherwise enriching the surface of the carbide with metal may be utilized. These may include, but are not limited to electroless plating, vapor deposition, thermal spraying as well as other techniques. In addition, other metals or metal alloys besides zinc may be utilized, including, but not limited to aluminum, magnesium, tin, cadmium and their alloys. Other metals, including iron and manganese and steel alloys can also be used. While the example discloses the use of a chromate conversion coating, it is acknowledged that alternative conversion coating processes can be used including oxide coating and phosphate coatings. Furthermore, while the example uses immersion to apply the conversion coating, other methods such as spraying or rolling may be used.

[0032] While the example given above details preferred embodiments such as solution concentrations, voltage and time requirements, it is acknowldedged that alternative values than those given in the example may also be used effectively. In addition, the exact formulas for soak baths may be altered by the use of acids other than those disclosed in the example.

[0033] A preparatory step can also be used prior to the metal plating, which can be used to better prepare the surface of the carbide part for the plating. While this step is not required, it may be used to improve the coloration procedure. This step involves the diffusion of cobalt from the binder of the bulk carbide part to the surface via a heat treatment operation. Through a carefully controlled heat treatment, typically performed in a molten salt bath or vacuum furnace, the suface of the carbide can become coated with a 4-6 micron layer of pure cobalt. While this treatment is often used to improve the brazeability of the carbide part, it can also be used as a pretreatment for the coloration process.

[0034] While the description of the invention contains specific information, this is not presented to limit the scope of the invention, but merely to provide an illustration of embodiments of the invention. The scope of the invention should be determined by the appended claims. 

1. A method for surface treating cemented carbide products comprising the steps of: a. enriching the surface of said product with a metal or metals, b. means for chemically coloring said metal-enriched surface of said product, c. rinsing and drying said product, whereby a color is imparted to the surface of said product such that said product can be easily visually distinguished.
 2. The method of claim 1 wherein said enrichment of the surface of the carbide product is done via electrolytic plating.
 3. The method of claim 1 wherein said enrichment of the surface of the carbide product is done via molten salt bath heat treating.
 4. The method of claim 1 wherein said enrichment of the surface of the carbide product is done via vacuum heat treating.
 5. The method of claim 1 wherein said means for chemically coloring the metal-enriched surface is done via conversion coating utilizing a solution comprised of one or more of a chromate, phosphate, or oxide.
 6. The method of claim 1 wherein said metal or metals contains one or more of zinc, cobalt, tungsten, iron, copper, aluminum, chromium, molybdenum, niobium, cadmium, nickel, magnesium, tin or manganese.
 7. The method of claim 1, wherein said colored surface of said carbide substantially degrades at elevated temperatures whereby the ability to braze the carbide is not substantially impaired.
 8. The method of claim 1 wherein said carbide product is pre-treated via a molten salt bath heat treatment.
 9. The method of claim 1 wherein said carbide product is pre-treated via a vacuum heat treatment.
 10. A method for surface treating cemented carbide products comprising the steps of: a. soaking said product in an acid solution, followed by a water rinse, b. plating the surface of said product by electrolytically depositing metal or metals from an acidic metal solution, followed by a water rinse, c. soaking said product in a chromate solution, d. rinsing and drying the product, whereby a color is imparted to the surface of said product such that said product can be easily visually distinguished.
 11. The method of claim 10 wherein the product is soaked in a dye after soaking in said chromate solution.
 12. The method of claim 10 wherein said carbide product is pre-treated via a molten salt bath heat treatment.
 13. The method of claim 10 wherein said carbide product is pre-treated via a vacuum heat treatment.
 14. The method of claim 10 wherein said metal or metals contains one or more of of zinc, cobalt, tungsten, iron, copper, aluminum, chromium, molybdenum, niobium, cadmium, nickel, magnesium, tin or manganese.
 15. The method of claim 10, wherein said colored surface of said carbide substantially degrades at elevated temperatures whereby the ability to braze the carbide is not substantially impaired.
 16. A method for surface treating cemented carbide products comprising the steps of: a. heat treating said product to effectively enrich the surface of the product with a metal or alloy from the binder of the cemented carbide, b. means for chemically coloring said metal-enriched surface of said product, c. rinsing and drying said product, whereby a color is imparted to the surface of said product such that said product can be easily visually distinguished.
 17. The method of claim 16 wherein said enrichment of the surface of the carbide product is done via electrolytic plating.
 18. The method of claim 16 wherein said means for chemically coloring the metal-enriched surface is done via conversion coating utilizing a solution comprised of one or more of chromate, phosphate, oxide.
 19. The method of claim 16 wherein said metal or metals contains one or more of of zinc, cobalt, tungsten, iron, copper, aluminum, chromium, molybdenum, niobium, cadmium, nickel, magnesium, tin or manganese.
 20. The method of claim 16, wherein said colored surface of said carbide substantially degrades at elevated temperatures whereby the ability to braze the carbide is not substantially impaired. 